1. Technical Field
This invention relates to the field of medical introducer apparatuses, and more particularly, to a medical introducer apparatus having longitudinally adjacent braid and coil reinforcing elements.
2. Background Information
Numerous advances of considerable note have occurred in medical surgical techniques over the last few decades. Among the most significant advances has been the adoption, and now-routine performance, of a wide variety of minimally invasive procedures. Non-limiting examples of such procedures include angioplasty, endoscopy, laparoscopy, and arthroscopy. These minimally invasive procedures can be distinguished from conventional open surgical procedures in that access to a site of concern within a patient is achieved through a relatively small incision, into which a tubular device (or tubular portion of a device) is inserted or introduced. The tubular device, or device portion, keeps the incision open while permitting access to the target site via the interior (i.e., lumen) of the tubular device.
Body passageways in which medical interventional devices are now commonly introduced include the esophagus, trachea, colon, biliary tract, urinary tract, and vascular system, among other locations within the body. One particularly significant example of a minimally invasive technique involves the temporary or permanent implantation of a medical interventional device, such as a stent, into a passageway in the body of a patient.
When placing the medical interventional device, communication with the passageway is typically attained by inserting an access device, such as an introducer sheath, into the body passageway. One typical procedure for inserting the introducer sheath is the well-known Seldinger percutaneous entry technique. In the Seldinger technique, a needle is initially inserted into the passageway, such as a vessel, and a wire guide is inserted into the vessel through a bore of the needle. The needle is withdrawn, and an introducer assembly is inserted over the wire guide into the opening in the vessel.
Typically, the introducer assembly includes an outer introducer sheath, and an inner dilator having a tapered distal end. The tapered end of the dilator stretches the opening in the vessel in controlled fashion, so that introduction of the larger diameter introducer sheath may then be carried out with a minimum of trauma to the patient. Following satisfactory placement of the introducer sheath, the dilator is removed, leaving at least the distal portion of the larger diameter introducer sheath in place in the vessel. The interventional device, such as an expandable stent, etc., may then be inserted through the introducer sheath for placement at a target site within the vasculature. Alternatively, the stent may be placed at the target site by withdrawing the introducer sheath from around the constricted stent. In either technique, upon placement at the target site, the stent expands to the diameter of the vessel.
Historically, percutaneous insertion techniques were problematic, due at least in large part to the lack of flexibility and/or kink resistance of the sheath. Early sheaths were typically formed of a relatively stiff fluorocarbon, such as polytetrafluoroethylene (PTFE) or fluorinated ethylene propylene (FEP). The sheaths were typically of thin-walled construction, and were prone to kinking, particularly when threaded through tortuous pathways within the body. Increasing the thickness of the sheath only minimally improved the kink resistance of the sheath. At the same time, the added thickness occupied valuable space in the vessel, thereby minimizing the diameter of the interventional device that could be passed therethrough. In addition, increasing the thickness of the sheath necessitated the use of a larger entry opening than would otherwise be required.
A kinked sheath is essentially unusable, and generally cannot be straightened while positioned in the body of the patient. Consequently, once a sheath kinks, the sheath must be removed from the vessel, leaving an enlarged, bleeding opening which cannot generally be reused. Access to the vessel must then be re-initiated at an alternative site, and the process repeated with a new sheath. In some cases, a suitable alternative site is not available, and the percutaneous procedure must be abandoned altogether in favor of a different, and often more intrusive, technique.
In recent years, introducer sheaths have been improved in order to enhance their flexibility and kink resistance. Such sheaths are now routinely used to percutaneously access sites in the patient's anatomy that previously could not be accessed with existing sheaths, or that could be accessed only upon the exercise of an undesirable amount of trial and error, with the concomitant discard of sheaths whose placement had been unsuccessful.
Many newer sheaths exhibit a much higher degree of kink resistance than was achievable with prior art sheaths. One example of a flexible, kink resistant introducer sheath is described in U.S. Pat. No. 5,380,304. The sheath described in this patent includes a lubricious inner liner having a helical coil fitted over the liner. An outer tube is connected to the outer surface of the liner through the coil turns. The coil reinforcement imparts kink resistant to this thin-walled sheath through a wide range of bending.
U.S. Patent Publication No. 2001/0034514 discloses an introducer sheath similar in many respects to the sheath of the '304 patent. The sheath in the patent publication is formed such that the proximal end of the sheath has a higher stiffness, while the distal end has a lower stiffness. Since the distal portion of the sheath has a lower stiffness (and therefore is more flexible) than the proximal portion, the sheath is able to traverse portions of the anatomy that would have been difficult, if not impossible, to traverse with stiffer sheaths. Since the proximal portion has a higher stiffness (and is therefore less flexible) than the distal portion, the sheath maintains the trackability to traverse tortuous areas of the anatomy. This presence of the coil reinforcement also enables this sheath to be kink resistant through a wide range of bending angles. These patent documents are incorporated by reference herein.
The development of introducer sheaths, such as those described above, has revolutionized the practice of medicine, and in particular, the ability of the physician to introduce medical interventional devices into target sites without the necessity of carrying out conventional open surgical operations. The percutaneous methods described are generally less expensive than the open surgical methods previously employed, are less traumatic to the patient, and typically require a shorter recovery time.
Notwithstanding the benefits that have been achieved by the use of such introducer sheaths, new challenges continue to be faced. For example, as noted above, introducer sheaths are frequently used for delivering an expandable device, such as a stent, filter, basket, etc., to a target site within a body passageway of a patient. In many such cases, these devices are placed (in constricted form) in the interior passageway of the sheath. Once the introducer sheath is properly positioned at the target site, the sheath is withdrawn from around the constricted device. Typically, an inner catheter (e.g., pusher) positioned in the lumen of the sheath prevents the device from withdrawing with the sheath. Upon withdrawal of the sheath, the device radially expands to the diameter of the body passageway at the target site.
Deployment of expandable devices, such as stents, in this manner is now a routine practice, and such deployment is often carried out with only a minimum of complications, if any. However, when devices such as coated and/or relatively long (e.g., at least about 80 mm in length) stents are placed in a sheath passageway in this manner for delivery, a high deployment force may be required due to the outward force exerted by such stents on the interior wall of the sheath. In this event, the coiled introducer sheath has a tendency to stretch longitudinally as it is withdrawn from around the stent. Although this phenomenon may also occur with non-coated stents or shorter stents, it is more pronounced with the coated and/or longer stents. Due to the extra diameter and/or length of these stents, a greater push force must typically be imparted by the inner catheter to overcome the tendency of these stents to remain with the sheath, as the sheath is withdrawn from the passageway. As a result, as the sheath is withdrawn over the stent, the resistance imparted by the stent may cause such sheaths to longitudinally stretch upon withdrawal.
Although such stretching may have no practical significance when shorter stents are positioned within the sheath, with longer stents, the stretching of the sheath causes the distance between adjacent turns of the coil to increase. This longitudinal expansion of the reinforcing coil adversely affects the ability of the sheath wall to withstand the radial expansive forces exerted on the interior of the wall by the stent. In addition, in some cases, the frame of the stent is able to push into this expanded distance between coil turns. When this occurs, a pocket may be created in the inner wall of the sheath. When the stent is disposed in this pocket, even more resistance is imparted upon the sheath upon withdrawal from the stent.
It is desired to provide an improved introducer apparatus suitable for traversing tortuous passageways in the patient's anatomy, and that is capable of minimizing the problems of the prior art. More particularly, it is desired to provide an introducer sheath that is capable of minimizing elongation or stretching during withdrawal of the sheath, thereby providing for more efficient withdrawal of the sheath when used to position a medical interventional device, such as an elongated stent, in a body passageway.